Repeated USMLE Questions Step 1- 308

A 26-year-old man presents to the clinic with a complaint of recurrent episodes of bloating, flatulence and diarrhea following eating dairy products. He mentions that he does not experience these symptoms if he does not drink milk or if he is fasting.

What is the most likely cause of diarrhea in this patient?






These symptoms indicate lactase insufficiency, known as lactose intolerance. Presence of non-absorbable osmotically active substance such as lactose in the intestinal lumen leads to osmotic diarrhea. Osmotic diarrhea also occurs after ingestion of magnesium-containing laxatives as Milk of Magnesium. Other types of diarrhea do not subside after fasting or avoiding dairy products which confirm the diagnosis of lactose intolerance.

The correct answer is B

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